Catalytic nickel plating



Feb. 3, 1959 H. R. NACK CATALYTIC NICKEL PLATING Filed Dec, 9, 1952 INVENTOR- HERMAN R. NACK BY Maw ATTORNEYS CATALYTIC NICKEL PLATIN G Herman R. Nack, Troy, Ohio, assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio Application December 9, 1952, Serial No. 324,963

2 Claims. Cl. 117-50 This invention relates to the deposition ofrnetals from the gaseous state. More particularlythe invention relates to the deposition of nickel from nickel carbonyls by thermal decomposition.

The deposition of nickel coatings on metals, such as iron and steels, has previously been practiced with varying degrees of success. Adhesion of the coating to the base metal, always a serious problem, has been achieved in a suitable manner for some applications. Efforts in the field have been directed to improving this adhesion in order that a product having a coating firmly bound to the base metal may be attained. These researches have considered the effects of various carrier gases for the carbonyls, the influence of flow rates, temperature, plating pressure, impurities, inter-gaseous decomposition, and so forth. The problem of securing a plate having suitable adherence to a base for all conditions of use however has remained present.

It has now been discovered that the adherence of the plating of nickel deposited from nickel carbonyl onto a base metal, such as iron and hot or cold rolled steels, may be materially improved, to the extent that a long thin sheet of the base when coated with nickel may be doubled upon itself without causing a buckling or separation of the coating from the base in any degree. In other words the coating and base remain completely integral under severe mechanical stress.

It is therefore a primary object of this invention to set forth a novel process for the deposition of nickel from nickel carbonyl.

It is a principal object of this invention to describe a novel treatment of a base metal prior to the introduction of the nickel carbonyl thereto.

It is a further object of this invention to describe a novel treatment of hydrogen gas to enhance the properties thereof for treatment of a base metal.

These and other allied objectives of the invention are attained, generally speaking, by utilizing a catalyzed hydrogen gas both as a cleansing medium and as a carrier gas for the nickel carbonyl in the plating process.

The hydrogen gas in accordance with the precepts of this invention is itself exposed to, that is, is passed over, what may be termed active nickel a process which in some not completely analyzed manner enhances the action of the hydrogen. Thus it has been discovered that if a base metal to be plated is heated to a temperature in excess of 500 F. and hydrogen which has passed over freshly deposited nickel is brought into contact with the base metal, the surface thus prepared is very receptive to the metal of the nickel carbonyl upon subsequent plating.

The active'nickel has'been referred to as freshly prepared; it is only necessary that the active nickel be pure metal-that isunoxidized. Generally speaking we have found that a nickel deposit which has been exposed to air over a weekend and consequently oxidized is ineffective to condition the hydrogen gas for the attainment of the objectives of this invention.

nited States Patent when plating the interior that the barrel itself be main- It is to be noted however that nickel metal which is unoxidized may be utilized repeatedly in the production of plated objects without apparent loss of efficiency.

Thus, for example, a gas plating chamber may be fitted with a hollow steel cylinder coated on the interior with deposited nickel which has not been exposed to the atmosphere and the nickel contents of this tube will serve indefinitely to catalyze the action of the hydrogen gas passing therethrough.

noted processes.

In the process of invention then the surface rendered receptive,-by the exposure of the heated base metal to the atmosphere comprising the hydrogen passed over the' active nickel, is, to effect metallic deposition thereon, ex

posed while heated to the action of hydrogen borne vapors of nickel carbonyl. wise passed over active nickel, that is, is exposed to the active nickel before or during the actual plating,

process.

An important feature of the present invention is that the object to be plated need not be raised to unduly high temperatures to effect either the cleaning or the plating operation; thus with gun barrels it is generally desirable tained at 750 F. or less. With the present invention the hydrogen gas passed over the active nickel may suitably and preferably be heated to much higher temperatures as 1200 F. to 1500 F., and then brought in contact with the surface to be plated to effect cleaning of the same; the body of the barrel may be at a much lesser temperature, that is 500 F. and the slowly flowing stream of hot hydrogen will not affect the body detrimentally.

The resultant etfect however is the attainment of a sur face eminently suitable for the receipt of the nickel coat.

The deposited nickel adheres tenaciously to the base metal and the thickness of the coat within normal limits has little or no effect upon the adhesion; this has been illustrated by preparing a thin coated sheet of hot rolled steel in accordance with the precepts of the invention and subjecting the sheet to severe bending sufficient to rupture the metal of the sheetthere was no apparent separation of the nickel from the base metal even at the rupture and the nickel could not be worked loose by prying at the same at the point of the rupture. Many processes for nickel deposition have been devised and investigated-but not coating prepared by other methods has withstood this rigorous test; in fact, no other gas plating method has provided a bond which is at all analogous so far as is known.

With regard to the process of invention generally the usual precautions must be observed to obtainthe improved adherent coat. Thus the object to be plated should be cleaned as thoroughly as possible prior to introduction to the plating chamber to remove surface oxides and other contaminants. Standard methods may be employed for this purpose and they include electro-etching chemical processes, abrasion or combination of these.

The nature of the metal to be plated determines to some extent the most satisfactory preliminary cleaning method. It has been found, for example, that hot rolled steel may be suitably prepared either by treatment with acid followed by an absolute alcohol wash or this chemical treatment may if desired be combined with an abra-' sion process. For cold rolled steel however the abrasion process is apparently necessary as this material does not respond quite as well when only the chemical treatment 2,872,342 Patented Feb. 3, 1959.

This gaseous mixture is likeis employed. Thus while not critical the abrasion process possesses more advantages with some metals.

The preliminarily cleaned metal is then placed in a plating chamber and the same is. exhausted to very low pressures. Where alcohol or equivalent material has been employed in the cleaning this is exhausted under vacuum. The exhaustion of the chamber and the removal of all occluded gas from the object is assisted by heating during evacuation-the heat being preferably ap plied though not necessarily by induction means.

The hydrogen gas is then bled slowly over the active nickel and to the object to be plated. The temperature of the objector base metal should be relatively highabove the normalplating range for nickel carbonyl.

The exact natureof the mechanism between the nickel and the hydrogen and the influence of the so-treated gas upon the base metal is not known. The hydrogen, if untreated, would as is. known tend to clean the metal surface by a reduction process. However the degree of adhesion attained by this latter known method is not at all comparable, all other conditions being the same, to the effect of the treated hydrogen, and this has been established by repeated testing of both methods under varying conditions.

It has been theorized that the nickel provides active atomic hydrogen to some extent which then affects the base metal surface favorably. This is supported in some degree by the fact that as the temperature of the nickel to which the hydrogen is exposed is increased results anpear to be more favorable. However even at the low temperature of 850 F. for the nickel improved results have been noted and for the presentthe explanation of the mechanism is in doubt.

The hydrogen is bled from a standard cylinder, treated and passed over the sample slowlya rate of about liter per minute measured at about 70 F. being satisfactory. The quantity and time vary somewhat with the size of the object but for a thin sheet 2" x 6" a time of. about 10 minutes is thoroughly effective. Vacuum pumps are applied during all of this time and consequently the chamber pressure ismaintained low assuring of rapid evacuation of all gases, that is, the hydrogen plus any impurities present. The application of vacuum is not however essential and the pressure in the chamber may be substantially or slightly greater than atmosphericthat is just sufiicient to insure of a hydrogen flow therethrough.

Thereafter nickel carbonyl in small quantity and the hydrogen, preferably but not necessarily mixed together, are passed over active nickel to the object. The temperature of the latter at this stage should be relatively high. that is, above 500 F., and the temperature may bepermitted to drop into the nickel carbonyl plating range of 250 'F.450. F. during the in-flow of the gases. Care must be exercised however to avoid excessive decomposition of the carbonyl and it has been found that such does not occur when the gases are flowed slowly, that is about 10-20 cc. per minute, and in small volume initially. Apparently the hydrogen inhibits premature carbonyl decomposition. As a result of this slow gas flow a thin film deposits on the activated metal surface, possibly resulting in diffusion of the nickel into the base metal as is indicated by the high degree of adherence attained.

It is. to be noted that all flow rates unless otherwise specified are measured at room temperature conditions- 76 F. and atmospheric pressures.

Asnoted during'the slow flow of hydrogen and nickel carbonyl the temperature of the object is allowed to fall into the normal plating range of the carbonyl; the flow rate is then increased to about 1 liter per minute at a suitable carbonyl concentration and'plating proceeds in normal manner, the entering gases however still preferably being passed through the active nickel, and where the active nickel is supported at a point remote from'the 4 workpiece the temperature of the nickel. should be. F. or less--that is below the plating range.

The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein:

Figure 1 is a schematic view illustrating a complete apparatus useful in the preferred embodiment of the invention;

Figure 2 illustrates a modification of the invention;

Figure 3 illustrates a structural arrangement useful in one modification of the invention;

Figure 4 illustrates yet another structure useful in a further modification of the invention; and

Figure 5 illustrates a rigid qualitative test for adherence of the coat to the base metal.

Referring to the drawings and particularly Figure 1 there is shown at 1 a glass vessel having a removable stopper 3, an inlet 5 and an outlet 6. A water jacket 7 having an inlet 9 and outlet 11 substantially surrounds vessel 1. Positioned at the right hand end of the vessel is a small platform 13 on which may be mounted the base metal or hot rolled steel object 15 to be plated. Positioned at the left hand end of the vessel is a tubular member 17 coated internally with active nickel 19, the tube being supported in the vessel in any suitable manner as by member 21. Suitable induction heating coils 22, 24 surround the tube at the area of the support 13 and the support 21, respectively.

A conduit 23- for the passage of hydrogen and a conduit 25 for the passage of nickel carbonyl are illustrated at the far left of the figure and it is clear that gases passing through these conduits will contact the nickel 19 in the passage of the gases to the hot rolled steel object 15. The outlet conduit 6 terminates in a U-shaped portion 27 surrounded by Dry Ice or other cooling liquid 29 contained in a tank 31. The outlet of the portion 27 is connected to a vacuum pump to hasten the removal of gases from the vessel 1.

In the operation of the apparatus indicated in Figure 1 with the vessel closed off by valve 33 the vacuum pump is operated to completely remove gases from the vessel. During'this period each of the coils 22, 24 may function to heat the interior components of the vessel to any suitable temperature to insure of the expulsion of all gases.

With valve 35 closed off valves 33 and 37 are opened to permit hydrogen to pass to the interior of the vessel 1. The temperature of the metal tube 17 and the nickel thereon is in excess of 850 F. and the upper limit is determined only by the temperature-limits which the materials involved will stand. The temperature of the ob ject 15 should also be in excess of 500 F. but may be considerably less than that of the cylinder 1'7. Specific data made under operating conditions are set out in the examples given hereinafter.

This arrangement of the apparatus ofiers the distinct advantage that in instances where the material 15 will not stand extremely high temperature, as in gun barrels, and where it is desirable to employ higher temperatures for cleaning, the hydrogen passing through the tube 17 may itself acquire a high temperature, thus increasing its activity to occasion'a very beneficial effect on the object 15. It has been found that this arrangement is superior in such instances to that where the temperatures of the cylinder 17 and the workpiece 15 are equal.

The hydrogen gas activated by the nickel apparently completely frees the object 15 of all impurities and the vacuum pump is maintained in operation during all of this period in order that impurities developed will be removed promptly.

It should be noted in connection with the hydrogen that the gas employed in the experiments described hereinafter is tank hydrogen containing not more than 0.15 by weight of water and not more than 0.15% by weight of oxygen, During the passage of the hydrogen in the course of the above described cleansing operation, there is no evidence whatsoever of any oxidation of the object 15 as long as the hydrogen flow is maintained relatively low, that is at about 0.1 liter per minute. Under some conditions of very high hydrogen flow rates, that is from 2 to 3 liters per minute, it has been found that a hot rolled steel piece may on occasion turn slightly blue indicating an oxidation effect and this is to be avoided. Normally the flow of hydrogen may continue for about minutes to secure the beneficial action but as higher temperatures are employed the action is faster and the time may be shortened accordingly. Upon completion of cleaning the heating of object is discontinued until the temperature falls to between 250 F.-450 F. and it is then maintained at this level until plating is complete. However, valve 35 is cracked open and nickel carbonyl is flowed into the hydrogen stream and the mixed stream of hydrogen and carbonyl pass over the nickel 18 as the temperature of the, object starts to drop. Some deposition of the nickel of the carbonyl gas may occur in the tube 17 but this is avoided to a great extent by initially flowing the gas very slowly, that is, at about 10-20 cc. per minute into the vessel 1. Concentration of the carbonyl is about 35 percent of the gaseous mixture and apparently the large hydrogen concentration inhibits nickel carbonyl decomposition to some extent since cloudiness characteristic of premature decomposition is at a minimum.

It is to be noted in this connection that any nickel deposited in the tube 17 at 19 tends to keep the nickel rejuvenated. However as a practical matter the deposition in this area is very small, if any, and the carbonyl together with the hydrogen passes onto the hot rolled steel piece 15 and nickel is deposited thereon.

The pump may be operated at all times during this initial flow of hydrogen and nickel carbonyl and the pressure is preferably maintained very low.

After the initial deposition of nickel the temperature of the workpiece is in the normal plating range of nickel carbonyl and is maintained at this level. The temperature of the nickel however is permitted to fall to 100 F. or less prior to heavy carbonyl flow to avoid excessive deposition at 17. The quantity of flow of hydrogen and the carbonyl is then increased to about 1 liter per minute the concentration of carbonyl being about 35%. The vacuum pump continues to operate in order to maintain the pressure within the vessel 1 low and nickel deposition continues to take place on the hot rolled steel piece 15 but at a faster rate. Some deposition may occur, as noted hereinbefore, at 19 but as indicated this is not detrimental in any respect. Upon completion of the plating to the desired thickness the stopper 3 is removed and the plated workpiece then taken from the chamber.

With the above described process a deposit of 3 mils may be obtained in about 20 minutes and other thicknesses may be obtained by merely increasing the time of plating.

It should be noted that the nickel 19 on cylinder 17 should not be exposed to the air during substitution of specimens or objects any longer than is necessary. Preferably to maintain optimum activity vacuum is maintained on the equipment as much as is possible.

The apparatus of Figure 1 and the operation above described is preferred because it permits of operation of the cylinder 17 at a materially different temperature than the object 15. However it is to be noted that as illustrated in Figure 2 there may be substituted for the cylinder 17 a platen 13 which supports a workpiece 15. This platen, preferably of steel, may be of any suitable metal coated with raised ridges of nickel in order. that the gases passing to the workpiece will contact the large surface of the nickel substantially as hereinbefore described.

It is also to be noted in connection with Figure 2 that the apparatus may if desired be operated without cooling.

In this instance however it is desirable to maintain the flow rates as low as is consistent with production purposes in order to avoid excessive premature decomposition of the carbonyl. Where such decomposition occurs it will result in an inferior coating as far as adhesion is concerned. While such an arrangement, that is, without a cooling chamber has been operated successfully it requires more attention and is not recommended in production operations.

The apparatus of Figure 2 illustrates that it is not essential that the gas flows contact the active nickel at any particular point of the system the mere presence of the active nickel during the hydrogen flow being sufiicient to produce an activated surface which is receptive to the initial flow of hydrogen and nickel carbonyl.

Figure 3 illustrates a metal tube 43 packed with steel wool 45 having thereon a deposit of nickel and this may be substituted for the cylinder 17 of Figure 1.

Figure 4 illustrates partially in section a similar metal tube 46, preferably of steel which contains suitably packed small steel balls 44 coated with nickel 47.

Figure 5 shows the manner of testing for adhesion and as will be noted a metal bar 49 (hot rolled steel) having a nickel coating 51 is severely bent to the point of fracture at 53. However even at the edge 55 of the break there is no apparent separation of the coat from the base metal.

The following examples illustrate the process of invention and it is to be understod that they are presented as illustrative only and not as limitative of the inventive concept:

Example I Utilizing the apparatus of Figure l the following conditions prevailed during the plating operation as sequentially indicated:

Workpiece (base metal)--- Hot rolled steel strip.

over 3 points on piece). Cylinder temperature (during hydrogen flow) 835 F. (maximum). Cool workpiece to temperature of 330 F.-350 F. Cool cylinder to temperature of Less than F. Hydrogen and nickel carbonyl (35%) while cooling 10-15 cc. per min. for 10 min.

Workpiece temperature Cylinder temperature Cool cylinder to lower than plating temperature"--- Maximum 100 F.

Maintain workpiece at 330 F.-350 F. Hydrogen and nickel carbonyl (35%) 1 liter per min.

It should be noted in connection with the foregoing that the initial introduction of hydrogen and nickel carbonyl at the rate of 10-15 cc. per minute occurs while the workpiece and cylinder are cooling and in fact while these members are above the plating range of nickel carbonyl. However when the major portion of the nickel carbonyl is introduced the cylinder must be below the temperature of plating of nickel carbonyl and preferably is about 100 F.

The above process permits the deposition of .010 in 1 hour and the deposit is. highly adherent as it withstands the test indicated in Figure 5.

Example 11 The arrangement of Figure 2 is utilized in connection with the following procedure:

Workpiece (base metal) Preliminary cleaning 850 F. maximum. 800 F.--900 F. 10 min. at ,5 liter per min.

750 F.850 F. (range over 3 points on piece). Platen temperature (during hydrogen flow) Cool workpiece and platen to temperature of Hydrogen and nickel carbonyl (35%) while cool ing l0-l5 cc. per min. for

min.

900 F. maximum.

workpiece temperature after carbonyl introductienufl Maximum 375 F.

Platen temperature after carbonyl introduction Maximum 400 F. Maintain workpiece and platen at 330 F.375 F. Hydrogen and nickel carbonyl (35%) 1 liter per min.

During the initial introduction of carbonyl and dur ing the platen operation itself some deposition of nickel on the nickel of the platen takes place. While this amount may be lost to production it serves to keep the platen rejuvenated and is accordingly beneficial in this respect.

An adherent deposit of about 3 mils may thus be obtained in about minutes.

Example 111 Workpiece (base metal) Cold rolled steel strip.

Preliminary cleaning Abrasion-plus degreasing in hot trichloroethylene treatment.

Heat up time 12 minutes. Workpiece temperature attained 1000 F. maximum Platen temperature 1100 F. Hydrogen flow 10 min. at ,3 liter per min.

Workpiece temperature (during hydrogen flow) 950 F.1050 F. (range over 3 points on piece).

Platen temperature (during hydrogen flow) 1200 F. maximum.

Cool workpiece and platen to temperature of Hydrogen and nickel carbonyl while coolin 10-15 cc. per min. for

10 min.

Workpiece temperature after carbonyl introduction Platen temperature after car- Maximum 375 F.

bonyl introduction Maximum 420 F. Maintain workpiece and platen at 330 F.3.'75 F.

Hydrogen and nickel carbonyl (35%) 1 liter per min.

In connection with the foregoing it is to be noted that preferable practice for the attainment of optimum adhesion includes the contact of the activated metal base surface with the initial carbonyl gas flow while the base is above the normal plating range of 250 F.-450 F. for the nickel carbonyl. Apparently such contact insures that completely repetitive results will always be attained as far as adhesion is concerned. On the other hand in one instance where the carbonyl was not passed to the workpiece until the same was at a temperature in the lower end of the plating range the coating was not up to the usual standard.

It is also to be noted with regard to the specific data on platen and workpiece temperature that such measurements were made by thermocouples the leads of which pass through the chamber walls; the slight variations in maximum temperature between the workpiece and platen where the same are on contact are occasioned by the contour of the coil with respect to these elements. As readings were taken at 3 points on each of the surfaces the figures set out are considered to be completely representative of actual conditions.

This application is related to copending application of Herman R. Nack et al., Serial No. 324,962, filed Dec. 9, 1952, now Patent No. 2,731,361, and assigned to the same assignee as the present invention.

It will be understood that this invention is susceptible to modification in order to adopt it to different usages and conditions and accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. A method of gas plating a deposit of nickel metal on the surface of a metal substrate to produce an adherent metal coating thereon which comprises the steps of heating said substrate to be gas plated in an enclosure, flowing hydrogen gas over substantially pure nickel metal and immediately thereafter bringing the thus pretreated hydrogen gas into contact with said metal substrate, and then contacting the thus treated substrate with gaseous nickel carbonyl while heated to a temperature sufficient to cause thermal decomposition of the gaseous metal carbonyl and deposition of a tenacious,

adherent coating of nickel onto the surface of said substrate.

2. A method of gas plating as in claim 1, and wherein the metal substrate is subjected to metal catalyzed hydrogen gas and wherein said hydrogen gas is flowed over heated substantially pure nickel which has been freshly deposited by the decomposition of nickel carbonyl.

References fitted in the file of this patent UNITED STATES PATENTS 1,497,417 Weber June 10, 1924 1,955,328 Frey Apr. 17, 1934 2,074,311 Moore Mar. 16, 1937 2,257,668 Becker Sept. 30, 1941 2,285,017 Christensen June 2, 1942 2,332,309 Drummond Oct. 19, 1943 2,344,138 Drummond Mar. 14, 1944 2,508,509 Germer et al. May 23, 1950 2,516,058 Lander July 18, 1950 2,731,361 Nack et al. Jan. 17, 1956 FOREIGN PATENTS 589,966 Great Britain July 4, 1947 OTHER REFERENCES Lander et al.: Plating Molybdenum, Tungsten, and Chromium by Thermal Decomposition of Their Carbonyls, American Institute of Mining and Metallurgical Engineers, Technical Publication Number 2259, September 1947,13. 30. 

1. A METHOD OF GAS PLATING A DEPOSIT OF NICKEL METAL ON THE SURFACE OF A METAL SUBSTRATE TO PRODUCE AN ADHERENT METAL COATING THEREON WHICH COMPRISES THE STEPS OF HEATING SAID SUBSTRATE TO BE GAS PLATED IN AN ENCLOSURE, FLOWING HYDROGEN GAS OVER SUBSTANTIALLY PURE NICKEL METAL AND IMMEDIATELY THEREAFTE BRINGING THE THUS PRETREATED HYDROGEN GAS INTO CONTACT WITH SAID METAL SUBSTRATE, AND THEN CONTACTING THE THUS TREATED SUBSTRATE WITH GASEOUS NICKEL CARBONYL WHILE HEATED TO A TEMPERATURE SUFICIENT TO CAUSE THERMAL DECOMPOSITION OF THE GASEOUS METAL CARBONYL AND DEPOSITION OF A TENACIOUS, ADHERENT COATING OF NICKEL ONTO THE SURFACE OF SAID SUBSTRATE. 